This invention has as its object new copolyimides with ether chain formations, and new adhesive compositions obtained by mixing or reaction of epoxy resins with said copolyimides with ether chain formations. The copolyimides, in addition to their utility as intermediates in the production of said compositions, themselves possess advantageous adhesive properties. Compositions obtained by mixing epoxy resins with said copolyimides are both thermoplastic and thermosetting, because the reactive functions of the epoxy resins induce crosslinking reactions at the moment the adhesive is used.
They further exhibit an entirely special solubility in numerous organic solvents, a very good resistance to heat and to oxidation and excellent adhesive properties.
The invention also relates to the use of these adhesive compositions as binders in the production of composite materials, such as insulating coatings, and such as adhesives for the gluing of metals or other materials. But because of their suppleness and their flexibility, they are particularly well suited for producing flexible composite materials. These materials can be obtained by gluing of films of organic polymers to one another or to thin metal sheets, or by gluing of films of polymers or of metal sheets to fabrics of organic or mineral fibers or further by gluing of metal sheets to one another.
It is known that the polyimides synthesized from aliphatic diamines as they have been described in U.S. Pat. Nos. 2,867,609, 2,880,230 and 2,944,993 are polymers generally having a thermoplastic nature, but requires relatively high temperatures, greater than 250.degree. C. and often between 300.degree. and 400.degree. C. Moreover, it has been demonstrated in U.S. Pat. No. 4,277,993 that, generally, polyimides of high molecular weight do not react with epoxy resins.
It has also been shown in French patent 2,514,772 that adhesive compositions made of an aromatic polybenzhydrolimide resin and an epoxy resin could be used to produce composite materials. Said compositions, however, have too great a structural rigidity to be used in applications which require a supple, flexible and elastic adhesive.
It is also found that the polyimides of the prior art, i.e., made by the reaction of a derivative of a tetracarboxylic aromatic acid with a diprimary aliphatic diamine, have thermoplastic properties at high temperature, but that they are not sufficiently flexible for certain specific applications such as gluing of supple materials. As will be seen in the comparative examples, these polymers have, in comparison with supple substrates, too great a rigidity which induces high mechanical stresses in the material. Further, since their temperature of thermoplasticity is generally greater than 200.degree. C., there are, at the moment the products are used, irreversible deformations of the substrates with large defects of surface evenness of the composite materials.